I previously mentioned the site http://www.assembla.com as a free site which offers a complete software development tooling suite (Subversion, Trac, Wiki, ...). The main benefit for us is that the students can form their own projectgroups and administer their own version control. This relieves me and our system administration of a lot of grunt work.
In the mean time the site has gone to a (very reasonable) commercial model but they still support students for free. Recommended!